Electronic systems are provided in an electrical apparatus, e.g. in an apparatus for a low or medium voltage application, to execute several tasks, for example power or control tasks.
For the purpose of the present description the term “medium voltage” is referred to electrical applications in the voltage range between 1 kV and some tens of kVs, e.g. 50 kV, while the term “low voltage” is referred to electrical applications having a voltage below 1 kV.
An electronic system can include one or more binary inputs, each adapted to receive an input and detect at least an electrical signal or command. The electronic system can include a controller associated with the binary inputs and adapted to execute various tasks according to the detection of the signals received by each binary input.
For instance, electronic systems with one or more binary inputs are used in switching devices, such as in switching devices for low or medium voltage circuits, e.g. circuit breakers, disconnectors and contactors, or in the switchgears or electrical cabinets where such switching devices are installed. For example, the binary inputs of such electronic systems are adapted to receive status information and/or commands for the associated switching device.
For example, the binary input can receive in input and detect a trip command generated into the switching device or received by remote. According to such application, the electronic system can be installed into the trip circuit of the switching device, such trip circuit having at least: a protection device, or relay, adapted to generate the trip command due to the detection of a fault condition; and an opening actuator, such as a coil actuator. The electronic system can be adapted (i.e., configured) to drive the opening actuator upon the detection of the trip command applied to the binary input, so as to open the switching device through the intervention of the opening actuator.
According to another exemplary application, the binary input can receive and detect an electrical signal indicative of an operative condition of the switching device, such as a signal indicative of the coupled or separated position of the contacts of the switching device itself.
Electronic systems with binary inputs have to withstand a large number of disturbances, some of which may possess a not negligible energy level.
Therefore, a noise or disturb signal can also be applied to and detected by the binary input as a signal generated for the electronic system, such as for causing execution of one or more tasks of the electronic system.
For this reason, a validation device can be associated to the binary input and function so as to validate the candidate signals applied thereto (which may be noise signals or signals generated for the electronic system).
The noise immunity of the electronic system, i.e. the capability of discriminating between a noise signal and a command or signal generated to be detected and validated, can strongly depend on the energy absorption performed by the electronic system, for example by the binary input, on the candidate signal applied to the binary input. For example, as demonstrated by electromagnetic measures and tests in laboratory, low noise immunity is associated with a low energy absorption performed by the binary input on the candidate signal applied thereto.
At the current state of the art the binary inputs are electronic circuits having associated high input impedance, so they are able to absorb only a very small amount of energy from the candidate signal applied thereto. Therefore, the validation function associated to a binary input could validate a disturbance or noise signal as a command or signal generated to be detected, compromising the correct working of the associated electrical apparatus.
For example, a disturbance signal may be applied to the binary input of an electronic system installed in the trip circuit of a switching device; since the binary input absorbs only a small amount of energy from the applied disturb, the associated validation function may validate such disturb as a valid trip command, generated for instance from the protection relay.
According to such validation, the electronic system drives the opening actuator to open the switching device, even if this opening operation has never been really requested.
At the current state of the art, the validation function associated to a binary input can be adapted to execute filtering operations, for example by using digital filtering techniques, to perform the signal validation; such as, the filtering time is set long in order to increase the noise immunity of the electronic system.
FIG. 1 illustrates for example a disturb signal 500 and a digital signal 501 generated to be detected and validated, which may both be a candidate input signal applied to a binary input of an electronic system known in the art. As shown in FIG. 2, when the application of such input candidate signal is detected at the detect time Tdetect, the validation device can start to filter the detected candidate signal for a long filtering time TF, and at the end of such filtering, validate the signal.
Setting a long filtering time can jeopardize the time response of the overall system, while in some applications, such as the control of the opening of a switching device, the electronic system has to execute its tasks as soon as possible after receiving a command or other relevant electrical information.
According to another known solution, one or more passive devices, such as resistors, are connected to the binary input in order to increase the noise immunity. The passive devices can be connected to the binary input so as to realize a passive load suitable for dissipating from the applied candidate signal an amount of energy which depends on the fixed impedance of such passive load.
The passive devices continuously dissipate power while the candidate signal is applied to the binary input, heating themselves and the other electronic devices placed on the same electronic board; such heating can become particularly critical when the candidate signal remains applied to the binary input for a long time, such as in applications wherein a signal is continuously provided to the binary input.
Therefore, at the current state of the art, although known solutions can perform in acceptable fashion, there is still desire for further improvements.